Handle fields with initializers in constant constructors.

pkg/compiler/lib/src/inferrer/type_graph_inferrer.dart

Index: pkg/compiler/lib/src/inferrer/type_graph_inferrer.dart
diff --git a/pkg/compiler/lib/src/inferrer/type_graph_inferrer.dart b/pkg/compiler/lib/src/inferrer/type_graph_inferrer.dart
index f81a6caaf604240ebd048d5a954e54b6e4fce99a..f8ae6eae90e378cef8487195db16b252e87127e3 100644
--- a/pkg/compiler/lib/src/inferrer/type_graph_inferrer.dart
+++ b/pkg/compiler/lib/src/inferrer/type_graph_inferrer.dart
@@ -856,20 +856,27 @@ class TypeGraphInferrerEngine
             if (constant != null) {
               ConstantValue value =
                   compiler.backend.constants.getConstantValue(constant);
-              assert(invariant(fieldElement, value != null,
-                  message: "Constant expression without value: "
-                      "${constant.toStructuredText()}."));
-              if (value.isFunction) {
-                FunctionConstantValue functionConstant = value;
-                type = types.allocateClosure(node, functionConstant.element);
+              if (value != null) {
+                if (value.isFunction) {
+                  FunctionConstantValue functionConstant = value;
+                  type = types.allocateClosure(node, functionConstant.element);
+                } else {
+                  // Although we might find a better type, we have to keep
+                  // the old type around to ensure that we get a complete view
+                  // of the type graph and do not drop any flow edges.
+                  TypeMask refinedType = computeTypeMask(compiler, value);
+                  assert(TypeMask.assertIsNormalized(refinedType, classWorld));
+                  type = new NarrowTypeInformation(type, refinedType);
+                  types.allocatedTypes.add(type);
+                }
               } else {
-                // Although we might find a better type, we have to keep
-                // the old type around to ensure that we get a complete view
-                // of the type graph and do not drop any flow edges.
-                TypeMask refinedType = computeTypeMask(compiler, value);
-                assert(TypeMask.assertIsNormalized(refinedType, classWorld));
-                type = new NarrowTypeInformation(type, refinedType);
-                types.allocatedTypes.add(type);
+                assert(invariant(
+                    fieldElement,
+                    fieldElement.isInstanceMember ||
+                        constant.isImplicit ||
+                        constant.isPotential,
+                    message: "Constant expression without value: "
+                        "${constant.toStructuredText()}."));
               }
             }
           }